This invention elates to heating, ventilating and air conditioning (herein HVAC) systems and in particular, to a field installable device for operating such systems more economical for air circulation. While the invention is described in detail with respect to HVAC applications, those skilled in the art will appreciate the wider applicability of the invention described below.
The user of conventional HVAC systems frequently chooses to let the system's blower operate continuously by setting the fan control switch on an associated thermostat to "on" position. This circulation mode of operation reduces temperature stratification, minimizes start drafts from duct work, improves humidity control, and increases the effectiveness of any associated air cleaners employed in conjunction with the HVAC system. By selecting the "on" position, the blower motor operates continuously, and the associated thermal feature, (i.e., either heating or cooling) operates on the "demand" setting of the thermostat.
Most present HVAC systems have provisions for operating the blower motor at one or more speeds The circulation or blower "on" mode of operation means the blower motor runs at the single speed for which the motor is configured for a particular thermal application. Generally the blower will operate at the highest set speed when the fan switch is "on". This speed usually is well in excess of what is necessary to achieve the benefits outlined above. This causes excess noise and energy usage. In addition, with the blower switch in the "on" position the unit no longer is able to select the system speed for cooling or heating. Even when systems are designed to select the proper speed in a multiple speed motor, for example, as disclosed in U.S. Pat. No. 4,815,524 ('524), the speed available for blower "on" use is higher than necessary for such operations, and can be responsible for cold spot corrosion, requiring the shut down period disclosed in the '524 patent.
More recently, HVAC systems have been designed to employ variable speed motors for blower control. While variable speed motors provide the desired results, their initial cost is high and they are not easily field installable without an additional electronic interface.
The invention disclosed hereinafter provides a motor and control, the control preferably being integrally constructed in the motor package. The motor and control are installable in conventional HVAC systems by field personnel. The control senses both the blower position setting and the thermal condition requirement called for by the thermostat The motor control combination allows a substantially lower speed during blower "on" operation, and the motor uses less energy than a conventional blower motor. That is to say, the motor of this invention allows lower, stable speeds at lower power consumption than motors of conventional designs for blower "on" operation. As a result, the pay back period for the modification to the HVAC system provided by the present invention is short, and easily recovered by the reduction in energy cost obtained in operational use.